The flower whose essential oil is widely used for calming and relaxation is lavender.
Lavender oil is distilled mainly from the flower spikes of Lavandula species, especially Lavandula angustifolia. It is a familiar ingredient in aromatherapy, perfumes, soaps, massage oils, and household products. Steam distillation separates the fragrant oil from harvested flowers and stems.
The oil contains many plant chemicals, with linalool and linalyl acetate among its dominant constituents. Its floral scent is strongly associated with rest and relaxation, and lavender oil is commonly used during massage or in diffusers. Research on aromatherapy has produced mixed results, so traditional use should not be presented as proof that it treats anxiety or other disorders.
Lavender is sometimes confused with chamomile, rose, or jasmine because all are fragrant flowers used in personal-care products. Lavender is the clearest canonical answer because its essential oil has an especially established association with calming and relaxation. Concentrated essential oils can irritate skin or be poisonous if swallowed.